The invention relates to a sprayer arrangement for the electrostatic coating of objects with liquid or powdery material. The sprayer is of the type which includes a pistol barrel, an atomizer nozzle located at the outlet of the barrel and fed with coating material via a feed line running in the pistol barrel. An electrode for charging the atomized material is connected to a high voltage generator by way of a high-impedance, current-limiting resistor in the gun and a high voltage cable running in or on the pistol barrel.
Such spraying arrangements particularly for spraying dyes or lacquers have been on the market in large numbers, whereby the high voltage electrode, perhaps in the form of a metal needle, is disposed in the atomizer nozzle or immediately adjacent thereto. The creation of an electric return line from the electrode via the dye or lacquer feed, the consequence of which being a considerable decrease of the charge voltage available at the electrode, is not to be feared in this case generally. This is so because the lacquers, or else the powders, have such a high electric resistance value that they can be designated almost as insulators. This is true even for known metal lacquers because in their case the individual metal particles are encased in the insulating lacquer.
Recently however, so-called water paints have come on the market, for example plastic paints, which are dilutable with water. These paints have such a high electric conductivity in the water-diluted state that they can no longer be sprayed electrostatically with the abovementioned known devices. This is because the electric current flow through the spray particles is so large that the voltage available is too low to create an adequate supply of electrostatically charged particles to provide the benefits of electrostatic spray coating. Expressed in other words, during spraying of such water paints, the necessary electrostatic high voltage field between the electrode and the object to be sprayed, and/or a ground, collapses. Moreover there is a danger of electric shuntings in the case of fouling of the spraying arrangement by the water paint occurring perforce during operation, a factor which not only decreases the operating efficiency of the device, but beyond that even endangers the operator.
One object of the invention is to minimize or obviate problems of the above-discussed type.
Another object of the invention is to improve the spraying arrangements of the initially mentioned type in such a way that it will be possible with them also to spray materials of considerable conductivity, especially also water paints, without trouble and danger electrostatically.